How Milk May Contribute to Childhood Obesity

We’ve known that breastfed infants may be protected against obesity later in life for more than 30 years, but why? It may be the formula. Giving infants formula based on cow’s milk presents an unusual situation. Cow’s milk is designed to put nearly two pounds a day onto a growing calf, 40 times the growth rate of human infants (see Formula for Childhood Obesity).

The perfect food for humans, finely tuned over millions of years, is human breast milk. Remarkably, among all mammalian species, the protein content of human milk is the lowest. The excessive protein content of cow’s milk-based formula is thought to be what sets the child up for obesity later in life.

And then, instead of being weaned, we continue to drink milk. The question, thus, arises as to whether consumption of a growth-promoting substance from another species throughout childhood fundamentally alters processes of human growth and maturation. A study out of Indiana University, for example, found evidence that greater milk intake is associated with an increased risk of premature puberty; girls drinking a lot of milk started to get their periods earlier. Thus, cross-species milk consumption and ingestion into childhood may trigger unintended consequences.

Only human milk allows appropriate metabolic programming and protects against diseases of civilization in later life, whereas consumption of cow’s milk and other dairy products during adolescence and adulthood is an evolutionarily novel behavior that may have long-term adverse effects on human health.

Teens exposed to dairy proteins, such as casein, skim milk, or whey, experienced a significant increase in BMI and waist circumference compared to a control group. In contrast, not a single study funded by the dairy industry found a result unfavorable to milk.

The head of the Obesity Prevention Center at Boston Children’s Hospital and the chair of Harvard’s nutrition department wrote an editorial recently to the AMA’s Pediatrics journal questioning the role of cow’s milk in human nutrition. They stated the obvious: humans have no requirement for other animal’s milk; in fact, dairy may play a role in certain cancers due to the high levels of reproductive hormones in the U.S. milk supply.